The present invention relates to a plasma processing apparatus for generating plasma by high-frequency electromagnetic fields to perform a predetermined process.
In manufacture of semiconductor devices and flat panel displays, plasma processing apparatus have been used widely and frequently for performing processes such as formation of oxide films, crystal growth in semiconductor layer, etching and ashing. Of the plasma processing apparatus as above, a high-frequency plasma processing apparatus is available in which high-frequency electromagnetic fields from an antenna are admitted to a process container to generate high-density plasma. This type of high-frequency plasma processing apparatus can generate plasma stably even when the pressure of plasma gas is relatively low and can be applied to widespread uses to advantage.
An etching apparatus using a conventional high-frequency plasma processing apparatus is constructed as shown in FIG. 20. In FIG. 20, the construction is partly illustrated in sectional form.
A dielectric plate 113 is disposed horizontally in an upper opening of a cylindrical process container 111. They are jointed to each other through the medium of a sealing member 112 to keep airtightness of the interior of the process container 111. Evacuation ports 114 for vacuum evacuation are formed in the bottom of the process container 111 and a nozzle 116 for gas supply passes through the sidewall of the process container 111. Housed in the process container is a carriage 122 for carrying a substrate 121 that is an object to be etched. The carriage 122 is connected to a high-frequency power supply 126 for biasing.
A radial antenna 130 is disposed above the dielectric plate 113. Peripheries of the dielectric plate 113 and radial antenna 130 are covered with a shield member 117.
The radial antenna 130 includes two mutually parallel conductive plates 131 and 132 forming a radial waveguide 136 and a ring member 133 for connecting outer peripheries of these conductive plates 131 and 132. A great number of slots 134 are formed in the conductive plate 131 constituting a radiation plane. When the wavelength of an electromagnetic field propagating inside the radial waveguide 136 (hereinafter referred to as a guide wavelength) is xcexg, pitch P2 between adjacent slots in the radial direction is set to be equal to the guide wavelength xcexg. An inlet port 135 for admitting the electromagnetic field to the inside of the radial waveguide 136 is formed in the center of the conductive plate 132. The inlet port 135 is connected with a high-frequency generator 145 through a waveguide 141.
The etching apparatus constructed in this manner operates as will be described below.
After the interior of the process container 111 is first evacuated to a predetermined degree of vacuum, a mixture gas of, for example, CF4 and Ar is supplied from the nozzle 116 under the control of flow rate. Under this condition, a high-frequency electromagnetic field is supplied from the high-frequency generator 145 to the radial antenna 130 by way of the waveguide 141.
While propagating inside the radial waveguide 136, the electromagnetic field supplied to the radial antenna 130 is radiated from the many slots 134 formed in the conductive plate 131. Since the pitch p2 between adjacent slots in the radial direction is set to xcexg, the electromagnetic fields are radiated in a direction substantially vertical to the conductive plate 131 (radiation plane). Then, the electromagnetic fields transmit through the dielectric plate 113 so as to be admitted to the inside of the process container 111.
Electric fields of the electromagnetic fields admitted to the process container 111 ionize the gas prevailing in the process container 111 to generate plasma in a space S1 above the substrate 121 representing the object to be processed. At that time, the electromagnetic fields admitted to the process container are not totally absorbed directly by the plasma generation but unabsorbed remaining electromagnetic fields repeat reflection inside the process container 111 to form standing waves in a space S2 between the radial antenna 130 and the plasma generation space S1. As is known in the art, electric fields of the standing waves also take part in the plasma generation.
The thus generated ions of plasma are extracted by negative potential at the carriage 122 and utilized for an etching process.
In the conventional etching apparatus shown in FIG. 20, the standing waves formed in the space S2 affect the plasma generation to a great extent. Since the distribution of the electric fields of the standing waves is difficult to control, plasma cannot be generated uniformly in the conventional etching apparatus. For example, through observation of plasma that is generated inside the process container 111 with the conventional etching apparatus, it is confirmed that portions 161A and 161B where plasma is generated at a high density take place near the center of a plasma generation region 160 as shown in FIG. 10A to be referred to later.
Consequently, the conventional apparatus faces a problem that the etching process proceeds more rapidly on the substrate 121 representing the processing object in underlying regions corresponding to the high-density plasma portions. The problem of causing spots in the processing amount is not specific to only the etching apparatus shown in FIG. 20 but is common to conventional plasma apparatus.
The present invention contemplates elimination of the above conventional problems and it is an object of the invention to improve the distribution of plasma generated by high-frequency electromagnetic fields.
To accomplish the above object, according to the invention, in a plasma processing apparatus using a slot antenna having a radiation plane formed with a plurality of slots so as to radiate electromagnetic fields to the inside of a process container through the plurality of slots, the slot antenna radiates the electromagnetic fields in a direction oblique to the normal direction of the radiation plane.
When a dielectric plate is disposed in parallel to the antenna radiation plane, the electromagnetic fields are radiated in a direction oblique to the normal direction of the dielectric plate. A plasma plane opposing the dielectric plate in the process container has a form extending along the dielectric plate and therefore, the electromagnetic fields directly incident upon plasma inside the process container from the slot antenna through the dielectric plate come into the plasma in a direction oblique to the normal direction of the plasma plane.
To explain briefly how an electric field of an electromagnetic field changes in a region ranging from the boundary between the plasma and dielectric plate to a point where the plasma density assumes a cut-off density, the intensity of a component of electric field in a direction parallel to the plasma plane is maintained to a substantially constant level but the intensity of a component of electric field in the normal direction of the plasma plane increases monotonously. Accordingly, by making the electromagnetic fields incident in a direction oblique to the normal direction of the plasma plane, a resultant component of the two components can take place having a higher electric field intensity than that obtained when the electromagnetic fields are made to be incident in the normal direction of the plasma plane. By virtue of this, the plasma generation efficiency attributable to the electric fields of the electromagnetic fields directly coming from the slot antenna can be improved.
Through this, contribution of the electric fields of the electromagnetic fields directly coming into the process container from the slot antenna to the plasma generation can be promoted and as a result, the participation of the electric fields of the standing waves (that is, indirectly incident waves) formed in the process container to the plasma generation can be reduced relatively. Since the former is controllable more easily than the latter, the distribution of plasma can be improved as compared to that in the conventional apparatus.
When in the aforementioned plasma processing apparatus the ratio xcex5v/xcex5a between specific inductivity xcex5v inside the slot antenna and specific inductivity xcex5a outside the slot antenna is xcex5r, the wavelength of the electromagnetic field propagating in the slot antenna is xcexg, the pitch between adjacent slots in the propagation direction of the electromagnetic field inside the slot antenna is defined as p=xcex1xc2x7xcexg (xcex1 greater than 0) and N is an integer not less than 0, the xcex5r, N and xcex1 may preferably be so set as to satisfy
xe2x88x921xe2x89xa6xcex5r1/2(N/xcex1xe2x88x921)xe2x89xa61
Nxe2x89xa0xcex1 for N being not less than 1.
Under this condition, the electromagnetic fields are radiated in a direction oblique to the normal direction of the radiation plane of the slot antenna.
The pitch between adjacent slots can be changed in the propagation direction of the electromagnetic field inside the slot antenna. In this manner, the radiation direction of the electromagnetic fields can be distributed in the radial direction in order to adjust the distribution of plasma.
Further, the apparatus may further comprise a dielectric member disposed to isolate the slot antenna from the carrying surface of the carriage and having a surface oblique to the radiation plane of the slot antenna. The dielectric member may take the form of a dome. The dielectric member may be for isolating at least part of the inner surface of the process container from the carrying surface of the carriage.
Alternatively, the apparatus may further comprise a first dielectric member disposed to isolate the slot antenna from the carrying surface of the carriage and having a surface oblique to the radiation plane of the slot antenna, a second dielectric member disposed, when referenced to the first dielectric member, on the side opposite to the carriage and being cooperative with the first dielectric member to form a hermetically closed space, and circulation means for circulating fluid through the hermetically closed space to adjust the temperature of the first dielectric member. The second dielectric member may be disposed either between the first dielectric member and the slot antenna or on the way of a feed line for the slot antenna.
As the slot antenna, a radial antenna may be used including first and second conductive plates mutually spaced to oppose to each other and a ring member for shielding the first and second conductive plates at their outer peripheries, wherein the first conductive plate is formed with a plurality of slots and an inlet port for admitting the electromagnetic field to a space between the first and second conductive plates is formed in the center of the second conductive plate. Also, a rectangular waveguide antenna including a rectangular waveguide having one surface formed with a plurality of slots may be used as the slot antenna.